The Khone Falls and Pha Pheng Falls is a waterfall located in Champasak Province on the Mekong River in southern Laos, near the border with Cambodia. The Khone Falls are the largest in southeast Asia and they are the main reason that the Mekong is not fully navigable into China. The falls are characterised by thousands of islands and countless waterways, giving the area its name Si Phan Don or 'The 4,000 islands'.

The average discharge of the cataract is nearly 11,000 m3/s, though the highest volume on record was reached at over 49,000 m3/s.

The falls are home to the plabuck, an endangered species of catfish said to be the largest freshwater fish in the world. The plabuck is alleged to reach lengths of 3 m (10 ft) and weights of up to 646 pounds (293 kilograms).